Former vice president Joe Biden speaks Tuesday in Ottumwa, Iowa. (Matthew Putney/AP)

Joe Biden told a climate change activist Tuesday he supported the idea of a presidential candidates’ debate focused on climate change, an idea pushed by climate activists that so far has been rejected by the Democratic Party.

“That’s what we should be doing,” the former vice president told a Greenpeace activist on a rope line after a speech here. “I’m all in, man. Take a look at what I’m talking about – and by the way, the first climate change plan in the history of the Congress? Biden.”

Biden has been at pains to emphasize his devotion to climate action, especially since an aide was quoted as saying Biden would take a “middle road” to fighting climate change — a characterization he strongly disputes.

Biden’s comment Tuesday made him the 15th Democratic candidate to endorse a debate focused specifically on climate change, a project of the Sunrise Movement and other green groups that has been championed by Washington Gov. Jay Inslee, who’s built his presidential campaign around the climate issue.

Some candidates have jumped at the chance to demand that the Democratic National Committee focus at least one of its dozen primary debates on an issue that was barely discussed in the 2016 debates. Many Democrats consider climate change a major crisis, and one that has been aggravated by President Trump, who pulled out of the Paris climate accord.

Other presidential hopefuls have endorsed the idea of such a debate when confronted by activists. Over the weekend, DNC Chairman Tom Perez, confronted at a party gathering in Orlando, told activists that it didn’t make sense to focus one debate on a single issue, suggesting there are many crucial matters for the candidates to address.

“It’s just not practical,” Perez said. “As someone who worked for Barack Obama, the most remarkable thing about him was his tenacity to multitask, and a president must be able to multitask.”

Inslee, however, has continued to pressure the DNC to host a climate debate. He has complained that the party threatened to punish any candidate who appears in an unofficial debate — including, say, one on climate change hosted by environmental groups — by excluding them from the official Democratic debates.

“The Democratic Party has an opportunity to host a debate and to send a clear message that we are the party of climate solutions,” Inslee said in a statement. “I’m calling on Chairman Perez to reconsider his decision, and on every 2020 candidate to clearly voice their opposition to the DNC’s decision to silence a climate debate.”